Great question! The amount of cardio necessary is highly dependent on my physique goals. During contest prep my body responds well to fasted morning cardio. My coach will adjust the times per week and duration throughout my prep in response to my conditioning. At the height of this past season I was doing 35 minutes of fasted cardio at a comfortable pace 6 days a week. I am currently in my off season and doing 20 minutes of fasted cardio 4 days a week at a comfortable pace. This is always subject to change dependent on my conditioning as well!
Remember, cardio is a very personal thing!! Everyone is different and some may require more or less cardio for their physique goals. Get that heart rate up and sweat it out! :D